X-ray fluorescence spectroscopy is divided into energy dispersive X-ray fluorescence analyzers and wavelength dispersive X-ray fluorescence analyzers depending on the dispersion method. The energy dispersive X-ray fluorescence analyzers use a low-power X-ray tube. Thus, the energy dispersive X-ray fluorescence analyzers can be implemented in a desktop configuration and a smaller size. However, the energy dispersive X-ray fluorescence analyzers do not have high analysis accuracy, and thus are not suitable for analysis of trace elements.
The wavelength dispersive X-ray fluorescence analyzers use a high-power X-ray tube. Thus, the wavelength dispersive X-ray fluorescence analyzers have high analysis accuracy, but require liquid nitrogen cooling, which increases the size and cost.
In recent years, as part of efforts to address environmental problems, the standard for trace sulfur (16S) as a harmful element contained in oil has been established, and regulation thereof is gradually becoming stricter. Along with this, a test method for ultratrace sulfur analysis is being standardized by the International Organization for Standardization (ISO) and the Japanese Industrial Standards (JIS). Thus, there is a demand for apparatuses capable of analyzing 0.5 ppm level (conventional quantitation limit) or less of sulfur in oil.
In order to satisfy such a demand, X-ray analyzers use a semiconductor detector having a large-area detection element.
However, using a high-power X-ray tube and a large-area X-ray detector requires utilities of large electric power, cooling water, and liquid nitrogen, etc., which increases the apparatus size and significantly increases the apparatus cost. Moreover, the installation area is increased, and a large space is required for installation. Frequent maintenance is also required, and maintenance cost of the apparatus is significantly increased.
It is a primary object of the present disclosure to provide an X-ray fluorescence spectrometer and an X-ray fluorescence analyzer using a spectroscopic system thereof, which can analyze 0.5 ppm level or less of a trace element in a measurement sample with high accuracy at relatively low cost.
It is another object of the present disclosure to provide an X-ray fluorescence spectrometer and an X-ray fluorescence analyzer using a spectroscopic system thereof, which reduces background of an analyzed element to improve the peak/background (P/B) ratio so that a trace element in a measurement sample can be analyzed.
It is still another object of the present disclosure to provide an X-ray fluorescence analyzer capable of analyzing the content based on the intensity ratio between fluorescence X rays and scattered X rays, and thus having further improved accuracy.
An non-limiting example X-ray fluorescence spectrometer (10, 20) according to the present disclosure includes: an X-ray source (21) that emits primary X rays to irradiate a sample to be measured with the primary X rays; a first spectroscopic unit (22) that disperses fluorescence X rays emitted from the sample; a second spectroscopic unit (23) that disperses scattered X rays scattered from the sample; and a single X-ray detector (24) that is positioned so as to be able to receive the fluorescence X rays dispersed by the first spectroscopic unit and the scattered X rays dispersed by the second spectroscopic unit, and that receives the fluorescence X rays and the scattered X rays.
The numerals in parentheses are the reference numerals of the corresponding elements in example embodiments.
According to the present disclosure, an X-ray fluorescence spectrometer can be obtained which is useful for analyzing 0.5 ppm level or less of a trace element in a sample with high efficiency at relatively low cost.
The fluorescence X rays and the scattered X rays emitted from the sample are dispersed and monochromatized into monochromatic beams by the first spectroscopic unit and the second spectroscopic unit, whereby a spectrum having a higher P/B ratio can be obtained. Moreover, the detection lower limit of the trace element in the oil can be 0.5 ppm or less, and analysis time can be significantly reduced.
The first spectroscopic unit may be formed to have a curved surface, and may be positioned so as to be able to collect the fluorescence X rays onto the X-ray detector. The second spectroscopic unit may be formed to have a curved surface, and may be positioned so as to be able to collect the scattered X rays onto the X-ray detector. The first spectroscopic unit, the second spectroscopic unit, and the single X-ray detector are thus selected so as to achieve an optimal optical arrangement. The X-ray detector may detect the collected fluorescence X rays and scattered X rays.
According to this configuration, an X-ray optical system of the spectroscopic units can be optimized, and the fluorescence X rays and the scattered X rays can be simultaneously detected by the single X-ray detector. Thus, detection accuracy of the fluorescence X rays can further be improved. The first spectroscopic unit may be a first analyzing crystal formed to have a curved surface, and is positioned so as to be able to collect the fluorescence X rays onto said X-ray detector and the curved surface is shaped so as to be tangent to a Rowland circle. The second spectroscopic unit may be a second analyzing crystal formed to have a curved surface, and is positioned so as to be able to collect said scattered X rays onto said X-ray detector and the curved surface is shaped so as to be tangent to a Rowland circle. The X-ray detector may be positioned at an intersection of said Rowland circle of said first analyzing crystal and said Rowland circle of said second analyzing crystal. By the structure the first analyzing crystal, the second analyzing crystal and the X-ray detector are arranged optically optimum and the X-ray detector detects the collected fluorescence X rays and scattered X rays.
The first spectroscopic unit may be placed between the sample and the single X-ray detector, and may guide the fluorescence X rays to the X-ray detector along a first path. The second spectroscopic unit may be placed between the sample and the single X-ray detector on a second path different from the first path, and may guide the scattered X rays emitted from the sample to the single X-ray detector along the second path different from the first path.
Preferably, the first spectroscopic unit is a first analyzing crystal, the second spectroscopic unit is a second analyzing crystal, the first analyzing crystal is selected so that a relation between a wavelength of an element to be measured, which is contained in the sample, and lattice spacing of a crystal material satisfies Bragg diffraction conditions, and so that the curved surface is shaped so as to be tangent to a Rowland circle, the second analyzing crystal is selected so that a relation between a wavelength of a target material of the X-ray source and lattice spacing of a crystal material satisfies the Bragg diffraction conditions, and so that the curved surface is shaped so as to be tangent to a Rowland circle, and the X-ray detector is placed at an intersection between the Rowland circle of the first analyzing crystal and the Rowland circle of the second analyzing crystal.
According to this configuration, efficiency of the X-ray detector is enhanced, and the detection accuracy can further be improved. Preferably, the X-ray detector is a semiconductor X-ray detector having energy resolution, and the semiconductor X-ray detector detects the collected fluorescence X rays and scattered X rays separately.
The X-ray source may be placed so as to irradiate a lower surface of the sample with the primary X rays, the first spectroscopic unit, the second spectroscopic unit, and the X-ray detector may be placed below the sample, and the X-ray detector may be a semiconductor X-ray detector.
According to this configuration, a detection error due to air bubbles can be reduced in the case where the sample is a trace element in liquid such as oil or water. Moreover, the use of the semiconductor X-ray detector allows a low output X-ray tube (several tens of watts) to be used, whereby reduction in cost can be implemented as compared to the case where a high output X-ray tube (several kilowatts or more) is used.
The non-limiting example X-ray fluorescence spectrometer may further includes: a third analyzing crystal (28) that is placed between the X-ray source and the sample, and that monochromatizes the primary X rays from the X-ray source to irradiate the sample with the monochromatized primary X rays.
The non-limiting example X-ray fluorescence spectrometer may further include: a first slit (25); and a second slit (26), wherein the first slit may be provided between the sample and the first spectroscopic unit on the first path, and may collect the fluorescence X rays emitted from the sample and guide the collected fluorescence X rays to the first spectroscopic unit, and the second slit may be provided between the sample and the second spectroscopic unit on the second path, and may collect the scattered X rays scattered from the sample and guides the collected scattered X rays to the second spectroscopic unit.
In another aspect of the present disclosure, an X-ray fluorescence analyzer includes: the X-ray fluorescence spectrometer described above; and a computation unit that obtains an intensity ratio between the fluorescence X rays and the scattered X rays detected by the single X-ray detector, and calculates a content of a trace element in the sample based on the obtained intensity ratio and a calibration curve.
In this aspect, an X-ray fluorescence analyzer can be obtained which is capable of analyzing 0.5 ppm level or less of a trace element in a sample with high accuracy at relatively low cost.
In still another aspect of the present disclosure, an X-ray fluorescence analyzer includes: an X-ray source that emits primary X rays to irradiate a sample to be measured with the primary X rays; a first spectroscopic unit that disperses fluorescence X rays emitted from the sample; a second spectroscopic unit that disperses scattered X rays scattered from the sample; a single X-ray detector that is positioned so as to be able to receive the fluorescence X rays dispersed by the first spectroscopic unit and the scattered X rays dispersed by the second spectroscopic unit, and that receives the fluorescence X rays and the scattered X rays; and a computation unit that obtains an intensity ratio between the fluorescence X rays and the scattered X rays detected by the single X-ray detector, and calculates a content of a trace element in the sample based on the obtained intensity ratio and a calibration curve.
Preferably, the computation unit includes a calibration curve table in which a result of obtaining the intensity ratio between the fluorescence X rays and the scattered X rays for every content in each of a plurality of samples having known contents of a trace element is registered in advance, a ratio calculating unit that obtains the intensity ratio between the fluorescence X rays and the scattered X rays of a sample having an unknown content of an element and detected by the X-ray detector, and a content calculating unit that calculates a content of a trace element in the unknown sample by referring to the calibration curve table based on the intensity ratio calculated by the ratio calculating unit.
The X-ray fluorescence analyzer may analyze a content of sulfur in oil.
In a further aspect of the present disclosure, an X-ray fluorescence analysis method includes: a step of placing an X-ray source that emits primary X rays to irradiate a sample to be measured with the primary X rays; a step of placing a first spectroscopic unit that disperses fluorescence X rays emitted from the sample; a step of placing a second spectroscopic unit that disperses scattered X rays scattered from the sample; a step of placing a single X-ray detector that is positioned so as to be able to receive the fluorescence X rays dispersed by the first spectroscopic unit and the scattered X rays dispersed by the second spectroscopic unit, and that receives the fluorescence X rays and the scattered X rays; and a computation step of obtaining an intensity ratio between the fluorescence X rays and the scattered X rays detected by the single X-ray detector, and calculating a content of a trace element in the sample based on the obtained intensity ratio and a calibration curve.
The computation step may include a first step of preparing a calibration curve table in which a result of obtaining the intensity ratio between the fluorescence X rays and the scattered X rays for every content in each of a plurality of samples having known contents of a trace element is registered in advance, a second step of obtaining the intensity ratio between the fluorescence X rays and the scattered X rays of a sample having an unknown content of an element and detected by the X-ray detector, and a third step of calculating a content of a trace element in the unknown sample by referring to the calibration curve table based on the intensity ratio calculated by the second step.
In a still further aspect of the present disclosure, an X-ray fluorescence spectrometer includes: an X-ray source that emits primary X rays; an analyzing crystal that monochromatizes the primary X rays from the X-ray source to irradiate the sample with the monochromatized primary X rays; a first spectroscopic unit that disperses fluorescence X rays emitted from the sample irradiated with the primary X rays monochromatized by the analyzing crystal; a second spectroscopic unit that disperses scattered X rays scattered from the sample; and a single X-ray detector that is positioned so as to be able to receive the fluorescence X rays dispersed by the first spectroscopic unit and the scattered X rays dispersed by the second spectroscopic unit, and that receives the fluorescence X rays and the scattered X rays.
According to this aspect, the background can be reduced. Thus, a peak of the fluorescent X rays can be made to appear, and high detection accuracy can be achieved. That is, using the monochromatized primary X rays as an excitation source can reduce the X-ray intensity of the background generated from the sample as much as possible, whereby a spectrum having a high P/B ratio can be obtained.
Preferably, the X-ray detector is a semiconductor X-ray detector having energy resolution, and the semiconductor X-ray detector detects said collected fluorescence X rays and scattered X rays separately.
According to the present disclosure, an X-ray fluorescence spectrometer and an X-ray fluorescence analyzer using a spectroscopic system thereof can be obtained which are capable of analyzing 0.5 ppm level or less of a trace element in a measurement sample with high accuracy at relatively low cost.
Moreover, an X-ray fluorescence spectrometer and an X-ray fluorescence analyzer using a spectroscopic system thereof can be obtained which reduces background of an analyzed element to improve the peak/background (P/B) ratio so that a trace element in a measurement sample can be analyzed. Furthermore, an X-ray fluorescence analyzer can be obtained which is capable of analyzing the content based on the intensity ratio between fluorescence X rays and scattered X rays, and thus having further improved accuracy